1. Field of the Invention
The present invention relates to a cutting apparatus for cutting large objects of different materials, such as stone, wood and other substances.
2. Background Art
Conventionally, cutting a large stone, for example, is carried out with a cutting blade, a band saw, a wire saw and other cutting methods.
Cutting blade is a device containing a plurality of cutting bits in which chips of abrasive grains, such as fine diamond abrasive grains are firmly embedded. The abrasive layers are bonded to an outer peripheral surface of a disc-like metal base formed by roll processing, by means of metal bond or the like at equal intervals. At present, the maximum cutting blade manufactured has a diameter of 3.5 m and a metal base thickness of 10 mm. For the cutting blade of this dimension or size, the maximum thickness of a material which can be cut is of the order of 1.5 m, and the cutting loss is of the order of 15 mm.
On the other hand, a band saw is a device having a thin strip of metal, which is wide and which is of the order of 1 mm to 6 mm in thickness, is welded to form an endless loop, and the abrasive grains and chips are firmly bonded to one side of the endless thin strip. The endless thin strip driven by a pair of rotating circular wheels, whose axes are arranged in parallel relation to each other. The wheels are rotated at high speed, thereby cutting stones or the like with the edge of any parallel sections between the rotor bodies.
The wire saw is an endless loop device such that a plurality of cylindrical diamond chips is firmly bonded to a metal wire whose thickness is of the order of a few millimeters to 10 mm. The wire saw is directly wound around the object, and is driven at high speeds with a constant tension applied by a drive apparatus, thereby cutting the object.
However, the above-described traditional cutting methods have the following problems.
First, the cutting blade has the following problem. That is, if the diameter of the cutting blade is increased, the thickness of the metal base must also be increased to provide the blade rigidity. For this reason, the cutting loss increases, and the yield from the object is diminished. Further, twist or torsion occurs at the forward edge of cutting as a result of an increase in the cutting resistance. Thus, the cutting accuracy is reduced.
Further, the cutting blade has also the following problems. Since manufacturing of a metal base exceeding 3.5 meter in diameter is extremely difficult, there is a limit in thickness of the object capable of being cut, as described previously. Moreover, such large cutting blade is extremely inconvenient for handling and transporting or the like; also the noises due to vibration at cutting are severe.
On the other hand, in the band saw, the metal base is thin and long in length, and the cutting loss is of the order of 4 mm to 8 mm which is relatively small. Thus, the yield is superior. However, the band saw is wound around a pair of large-diameter rotating wheels, and accordingly, the cutting apparatus increases in size, and a large equipment space is required.
Furthermore, the band saw has the following problem. That is, bending stress is repeatedly applied to bent sections of the metal base wrapped around the rotating wheels and metal fatigue is apt to be accumulated in the metal base. Thus, the metal base is broken relatively prematurely, and the service life of the metal base is short.
In the wire saw, since the chips in the abrasive-grain-layer are large in diameter, the cutting allowance must be large in comparison with the size of the cutting blade or the band saw. Further, the wire saw is circular in cross-section, and has, by itself, no means for restricting the cutting direction. Accordingly, the wire saw is inferior to other cutting methods in flatness and surface roughness of the cut surface. Furthermore, in the wire saw, since large bending stress is applied to both end portions of each of the abrasive-grain-layers during cutting, the service life is short. Breakage of the wire is dangerous because the ends of the wire jumps up and down like a whip.